A printer to print an image on a print medium having a thermosensitive layer includes a print head having a plurality of heating elements. The heating elements are arranged along a direction of a print line. Such a printer causes each heating element to generate heat independently by applying voltage separately to each heating element. When the print medium is heated by the heat-generating heating element, the thermosensitive layer of the print medium is colored for each print line. Thus, an image is printed on the print medium.
For printing a pictorial figure (e.g., a filled rectangle or ruled line) having many print dots on a single print line, it is required to cause many heating elements to generate heat at the same timing. Accordingly, power consumption of the printer becomes large. Recently, such power consumption is required to be suppressed. In particular, usable power is restricted with respect to remaining battery charge for a portable printer operating with a battery. Accordingly, power consumption is strongly required to be suppressed.
Conventionally, as a technology to suppress power consumption for printing a pictorial figure having many print dots on a single print line, there has been known a technology that a plurality of heating elements is divided into a plurality of groups and the heating elements generate heat at different timings for each groups (e.g., Japanese Patent Application Laid-open No. 2009-148948).